Application of SDS2000 in Switching Power Supply Analysis

Power supply is an indispensable part of all electronic products. Power supply is divided into switching power supply, linear power supply and other types. Among them, switching power supply has become the mainstream architecture of power supply in digital computing and network communication systems. The quality of switching power supply is related to the overall performance of the product. Therefore, accurate analysis of power supply is particularly important in R&D and production testing. SIGLENT's SDS2000 super fluorescent oscilloscope is equipped with a powerful power supply analysis module, which supports accurate test and measurement of most power supply performance indicators. The following will introduce the power supply analysis function of SDS2000 in detail by analyzing the power board input module.

Taking the power supply demonstration board STBX as an example, its physical view is shown in Figure 1:

Figure 1 STBX

The STBX circuit schematic is shown in Figure 2:

 Figure 2 Schematic diagram

Before any operation, you should first check whether the oscilloscope and power supply demonstration board are operating properly. After ensuring that the oscilloscope, power supply demonstration board, probe and other required items are in good condition, start power supply analysis.

First, we use SDS2304, differential probe, and current probe to measure the waveform of the power input terminal and obtain the results as shown in the following figure (Figure 3). The purple-red curve of channel 2 represents the voltage waveform, and the green curve of channel 4 represents the current waveform. Through the powerful parameter measurement function of SDS2000, we can easily obtain the peak-to-peak value, effective value, maximum value, minimum value, etc. of current and voltage. The measurement items in the figure are the peak-to-peak value and frequency of current and voltage.

Figure 3 Input primary signal

Since each specific voltage and current probe has different propagation delays, the timing delay error between the voltage and current probes will have a great impact on the power measurement. Therefore, in order to perform accurate power measurements and calculations, we must use the "delay offset correction" procedure to balance the delay between the voltage and current probes during actual operation. This step is very important. By performing probe delay offset correction before measuring power, accurate measurements can be ensured.

Figure 4 Power supply analysis items

As shown in the figure above (Figure 4), SDS2000 is equipped with a powerful power analysis module. In the power analysis, you can choose a variety of different analysis methods such as power quality, current harmonics, inrush current, switching loss, conversion speed, modulation, output ripple, transient response, etc. This allows engineers to have more flexible choices and greater operating space in practical applications. This article will focus on power quality analysis, current harmonic analysis, and inrush current analysis. Power quality analysis can measure important indicators of power quality such as power and phase angle. Part of the AC current can flow into or out of the load without providing energy. This current is called reactive current or harmonic current, which can generate "apparent" power that is higher than the actual power consumption. Power quality is measured by the following measurement values: power factor, effective power, apparent power, reactive power, crest factor, current phase angle, and AC line voltage, as shown in the figure below (Figure 5).

Figure 5 Analyzable parameters

The measurement parameters display interface is as follows:

Figure 8 Phase angle

As can be seen in Figures 6, 7, and 8 above, SDS2000 uses the MATH calculation function, combined with the powerful measurement statistics function, to easily obtain the much information we need, and can accurately display the current value, average value, minimum value, maximum value, and standard deviation of the measurement item at the same time. It provides a more efficient and convenient experience for engineers. Next, we need to analyze the current harmonics, select the current harmonics, set the signal frequency type to 50Hz, and select the standard as Class A. As shown below:

Figure 10 Setting signal frequency and current harmonic standard type

When we choose a current harmonic standard, we must first understand the differences between the standards.

Class A: Applicable to balanced three-phase equipment, household appliances (except Class D equipment), tools (except portable tools), incandescent lamp dimmers and audio equipment;

Class B: Suitable for portable tools;

Class C: Applicable to lighting equipment, Class C requires a power factor calculation when pressing the "Apply" softkey (in the "Power Application" main menu), so when "Power Application" is disabled, only Class C can be selected, which forces you to press "Apply" again to perform the analysis;

Class D: Applicable to equipment with a rated power less than or equal to 600 W, the following types: personal computers and personal computer monitors, television receivers.

After the settings are completed, open the FFT operation function in MATH, select the Hanning window type, select the table display in the display, and press the "Apply" button. After the analysis is completed, the result diagram of the current harmonic analysis can be obtained as shown below (Figure 11):

Figure 11 Current harmonic analysis

It can be seen that the current table displays 8 harmonics with a harmonic frequency of 50Hz~400Hz. At the same time, the current effective value (RMS), limit value (RMS), margin (Margin) and pass/fail status can also be observed. In the figure, the corresponding harmonic margins of 100Hz, 200Hz, and 300Hz are <80%, which is counted as Fail, while the rest are Pass (Note: the margin calculation method is {(limit value-actual value)/limit value}*100%). In practical applications, more observable harmonics will lead to more accurate power supply parameter analysis. SDS2000 inrush current analysis can measure the power supply inrush current and record the current waveform. The peak current can be positive or negative, so the result is the larger of the maximum or minimum values ​​measured.

The measurement results are shown below (Figure 12):

Figure 12 Inrush current measurement

As Dingyang's first super fluorescent oscilloscope that adopts the original SPO technology, SDS2000 has a high processing speed, powerful measurement and statistical functions, and is equipped with a powerful power analysis module. It is a sharp sword in power analysis. While adding multiple measurement indicators, it simplifies operations and optimizes the interface, making it more convenient and efficient for engineers to use.

As a professional digital oscilloscope and other general instrument manufacturers integrating R&D, production, sales and service, SIGLENT has always focused on the R&D and manufacturing of the latest test and measurement instruments, insisting on R&D as its core competitiveness. Through continuous technological innovation and strict quality control, SIGLENT gradually deepens its brand building. We have reason to believe that SIGLENT will continue to bring more, better and more practical products in the future.